A clutch is a device that connects and disconnects a pair of concentric rotary shafts easily and rapidly. The clutch is generally between a motor and an input shaft transmitted to a machine to operate or stop the machine, and causes an engine to operate in non-load state as in cars.
A clutch used in commercial cars has a power transmission function to transmit a rotating force of the engine to the transmission and a power shut-off function to temporarily block the power flow between the engine and the transmission whenever required, allowing smooth starts without vibration, protects the engine and the power transmission device against overloads, and reduces rotational vibrations of the engine together with the flywheel.
FIG. 1 shows a structure of a conventional general clutch device. As shown in FIG. 1, the clutch is configured to mainly include a clutch pedal 1 which receives a manipulation force of a driver, a master cylinder 3 which transmits the force of the clutch pedal 1, an air pump 5 which is connected to the master cylinder 3 to supply air pressure, a booster cylinder 7 having a piston rod 7a which operates with the air pressure supplied by the air pump 5, a release cylinder 9 which operates a clutch 11 with the air pressure supplied by the booster cylinder 7, a shift lever 13 hinged to the release cylinder 9 to connect the release cylinder 9 to the clutch 11. A push load 9a of the release cylinder 9 has a restoring force by a spring 9b. 
In the clutch configured as above, when the driver steps on the clutch pedal 1, the force operates a piston rod 3a of the master cylinder 3 so that air pressure supplied by the air pump 5 is introduced into the booster cylinder 7 through an air pressure guiding unit 51, then the introduced air pressure moves the piston rod 7a of the booster cylinder 7, causing the push rod 9a of the release cylinder 9 to move, and with the movement of the push rod 9a, the shift lever 13 disengages a clutch disc of the clutch 11 from a driving plate of the engine, to cut off the power transmitted to the wheels.
However, the clutch must operate the clutch pedal numerously while the car stops and goes at low speeds repeatedly for a long time or drives in city, which aggravates fatigue of the driver and places strain on the driver's knees and waste.
Also, to avoid stalling the car, when the driver takes his/her foot off the clutch pedal, the driver needs to step on the accelerator pedal with a delicate foot motion for a half clutch period, and in this instance, if the driver takes his/her foot off the clutch pedal prematurely, the car shakes or the engine stalls, and on the contrary, if the driver takes his/her foot off the clutch pedal too late, power is not properly transmitted to the car, resulting in failure to driving control of the car.
To solve this inconvenience, an automatic transmission achieving automatic shifting is mounted, and in this case, advantages are convenience and comfort the driver feels during driving, but disadvantages are increases in initial purchasing price, and increased fuel consumption by about 20-30% during driving as compared to a manual transmission.
In the case of existing commercial manual cars, when the foot is taken off the accelerator pedal during driving, fuel is supplied to the engine and consumed in proportion to the driving speed (RPM), and as a solution for reducing fuel, coasting in neutral on a hill is considered, but there are inherent problems with accident risks, for example, non-application of engine braking and stopping distance.
To solve this problem, many concepts of semi-auto clutches have been proposed, but their structure is complex, causing the problem with subsequent repair and maintenance, and process of attaching to existing cars is complex. Accordingly, a clutch control apparatus with a structure that allows attaching and detaching to/from existing cars in a simple manner and convenient repair and maintenance is required.
Particularly, in the case of conventional semi-auto clutches, as a clutch operation is controlled using a motor, its rotation value is read from a potentiometer and converted to a straight line displacement value, and a clutch clearance is calculated and used for transmission control, and to this end, machinery size increases, making it difficult to mount in cars.
Furthermore, unnecessary transmission impacts occur due to an error through mechanical SLIP in the process of converting the rotation value to displacement.